Aircraft navigational assistance method and corresponding device

ABSTRACT

The invention relates to a method of automatic navigation assistance for an aircraft. A capture zone being a zone in which the aircraft can capture a predetermined vertical profile segment by applying a transition between the guidance submode which the aircraft is in and the guidance submode adapted to the following of the vertical profile segment to be captured, it comprises the step consisting in determining the width of the capture zone as a function of the height h of the vertical profile to be captured and of the speed v which the aircraft has when plumb with this height when the aircraft is not on the profile or at this height when the aircraft is on the profile.

The invention relates to a method and a device for assisting navigation.

The field of the invention is that of assistance with aerial navigationand aerial safety and relates more particularly to assistance with themonitoring of the guidance of an aircraft along a trajectory within theframework of automatic flight control.

It may involve a descent trajectory or climb trajectory. In whatfollows, a descent trajectory will be taken as an exemplary trajectory,and an airplane will be taken as an exemplary aircraft. Such atrajectory 1 represented in FIG. 1 and called the vertical profileconsists of a succession of rectilinear segments and is decomposed intotwo parts: a first part 10 during which the airplane is relatively freeand which may therefore be optimized by adopting a preset speed and athrust making it possible to minimize the consumption of fuel and asecond part 11 for preparing the airplane for approach and for landingon a runway 12 during which the airplane must comply with certainparameters relating to altitude, speed and horizontal course by adoptinga constrained speed and a constrained slope.

An airplane descent trajectory is computed in reverse starting from theconfiguration of the airplane on landing, then by backtracking and byestablishing from point 2 to point 2 the corresponding speed preset andthrust preset until the point at which the descent begins or “TOD”, theacronym standing for “Top of Descent”.

Once this profile has been established by the flight management system(FMS) on the basis of constraints given by the air traffic controllers,the flight management system will give orders to the automatic pilot tojoin up with this profile and hold there, these orders being establishedas a function of control laws and of speed and thrust presets specificto the profile segment.

A distinction is made between the laws which determine the control ofthe elevators as a function of presets for speed (SPD), for verticalpath (VPATH) or for vertical speed (VS) and the laws which determine thecontrol of thrust and which are established as a function of presets forthrust (THR) or for speed (SPD). These laws are combined together andthe resulting pairs of laws associated with guidance submodes, make itpossible to establish the orders which will allow the aircraft to joinup with (or stated otherwise capture) the profile segment or to holdthere while complying with certain constraints.

From the above, the zone in which it is possible to capture the profileby applying a transition between the guidance submode which the airplaneis in and the guidance submode adapted to the following of the profilesegment to be captured is designated as the zone of capture about theprofile. Outside of this zone a guidance submode making it possible tojoin up with this capture zone as quickly as possible is applied.

This capture zone 3 represented in FIG. 2 may be defined as a band ofdiameter D, fixed or depending only on the speed, centered on theprofile 1.

However these definitions take no account of the differences inparticular between a flight at high altitude and high ground speed (atthe start of a descent for example) and a flight at low altitude and lowground speed (during for example the preparation for the approachprocedure), as well as the corollaries such as flights at low altitudeand high ground speed.

Thus for a flight at high altitude and/or at high speed, the capturezone is too restricted and the capture of the intended profile segmentis too fast in particular for the comfort of the passengers; likewisefor a flight at low altitude and/or at low speed, the capture zone istoo wide and the capture of the intended profile segment is too lengthyin the sense that part of this capture time could have been devoted toanother mode of flight and in particular to a faster capture with a morefuel-economical mode of flight such as for example the “airmass” mode.

Finally, the execution of the orders by the automatic pilot do notalways make it possible to ensure the comfort of the passengers or toadopt a suitable mode of flight, during the capture of the profile.

It is known that, in order to ensure the comfort of the passengers, themovements of the aircraft must not lead to the vertical accelerationfactor exceeding a certain threshold, for example equal to 0.1 g, gbeing the terrestrial acceleration (g=9.81 m/s²=32.1725 ft/s²). Thisfactor must not be exceeded during capture either.

As a result, in order to ensure the comfort of the passengers, it isnecessary to force the capture of the profile through trajectoriessubject to constrained load factors. The shape of the trajectory makingit possible to preserve a constant vertical acceleration factor duringcapture is a parabola tangential to the profile.

To ensure the comfort of the passengers, it is also necessary to avoidbig variations in thrust.

An important aim of the invention is therefore to choose a capture zonethat is better adapted to the comfort of the passengers and to fastnessof capture than in the prior art.

To achieve these aims, the invention proposes a method of automaticnavigation assistance for an aircraft, principally characterized in thata capture zone being a zone in which the aircraft can capture apredetermined vertical profile segment by applying a transition betweenthe guidance submode which the aircraft is in and the guidance submodeadapted to the following of the vertical profile segment to be captured,it comprises the step consisting in determining the width of the capturezone as a function of the height of the vertical profile to be capturedand of the speed which the aircraft has when plumb with this height whenthe aircraft is not on the profile or at this height when the aircraftis on the profile.

A subject of the invention is also a device for automatic navigationassistance for an aircraft comprising at least one program memory,characterized in that the program memory comprises a program forcomputing the width of a capture zone, a capture zone being a zone inwhich the aircraft can capture a predetermined vertical profile segmentby applying a transition between the guidance submode which the aircraftis in and the guidance submode adapted to the following of the profilesegment to be captured, the width of the capture zone being calculatedas a function of the height of the vertical profile to be captured andof the speed which the aircraft has when plumb with this height when theaircraft is not on the profile or at this height when the aircraft is onthe profile.

Other characteristics and advantages of the invention will becomeapparent on reading the detailed description which follows, given by wayof non limiting example and with reference to the appended drawings inwhich:

FIG. 1 already described diagrammatically represents a vertical profile,

FIG. 2 already described diagrammatically represents a capture zoneaccording to the state of the art,

FIG. 3 diagrammatically represents a capture zone according to theinvention,

FIG. 4 diagrammatically represents a device for assisting navigationaccording to the invention.

The problem posed is to determine the capture zone and more precisely todetermine it in an optimal manner as a function of the dynamics of theairplane and of the comfort of the passengers.

More precisely, this involves determining this capture zone in such away that it is wider for a flight at high altitude and/or high speed andless wide for a flight at low altitude and/or at low speed.

The method according to the invention is based on the computation of thewidth of the capture zone also referred to as the margin, as a functionof the height of the vertical profile to be captured and of the groundspeed that the airplane has when plumb with this height when theaircraft is not on the profile or at this height when the aircraft is onthe profile.

According to a particular embodiment of the invention, this function isdetermined from the law regarding the total mechanical energy, such thatE_(t)=E_(c)+E_(p).

E_(t), E_(c) and E_(p) respectively being the total energy, the kineticenergy and the potential energy of the airplane.

As represented in FIG. 3, by designating the ground speed that theairplane has on the profile at the height h or plumb with this height byv, its mass by m, the height of the upper bound of the capture zone byh′ and the height of the lower bound by h″, and by defining theequivalent total height ht arising from the total energy, we put:${E_{t} = {{mgh}_{t} = {{\frac{1}{2}{mv}^{2}} + {mgh}}}},{{i.e.\quad h_{t}} = {\frac{v^{2}}{2g} + h}}$According to an embodiment of the invention, the margin is thenexpressed according to a function of the total height by considering asafety height h_(s) and an adaptation constant K varying according tothe characteristics of the airplane:${\Delta\quad h} = {{h^{\prime} - h} = {{h - h^{''}} = {{h_{s} + {\frac{1}{K}h_{t}}} = {h_{s} + {\left\lbrack {h + \frac{v^{2}}{2g}} \right\rbrack\frac{1}{K}}}}}}$K allows Δh to vary between h_(s), for a flight at low altitude and lowspeed, and a limit height for a flight at high altitude and high speed,regardless of the ground speed v and the height h.

The method described is implemented in an onboard device for assistingthe navigation of an aircraft. An example of this device 100 isrepresented in FIG. 4. It comprises in a conventional manner one or moremicroprocessors 101 coupled to a program memory 102 of ROM type forexample, to a work memory 103 of RAM type for example and to one or morememories 104 of ROM type for example for the storage of the verticalprofile to be captured, as well as circuits 105 for transferring databetween these various elements. The program memory 102 contains theprogram that runs the method, in the form of source code, whereas thework memory 103 comprises registers that can be updated for the storageof the results of the computations. This equipment 100 also comprises acommunication interface 106 for allowing the exchange of data withdevices such as for example with a user interface 107, with sensors,etc.

These elements are for example included in a flight management system(FMS). They may also be included in the form of dedicated integratedcircuits, designed to implement the method.

1. A method of automatic navigation assistance for an aircraft,comprising the steps of: aircraft capturing a predetermined verticalprofile segment aircraft in a capture zone; applying a transitionbetween a guidance submode which the aircraft is in and the guidancesubmode adapted to the following of the vertical profile segment to becaptured; and determining the width of the capture zone as a function ofthe height h of the vertical profile to be captured and of the speed vwhich the aircraft has when plumb with this height when the aircraft isnot on the profile or at this height when the aircraft is on theprofile.
 2. The method as claimed in claim 1, wherein the width of thecapture zone is determined as a function of the height h and of thesquare of the speed v.
 3. The method as claimed in claim 1, wherein thewidth of the capture zone is equal to around 2Δh with${\Delta\quad h} = {{h^{\prime} - h} = {h_{s} + {\left\lbrack {h + \frac{v^{2}}{2g}} \right\rbrack\frac{1}{K}}}}$h′ being the height of the upper bound of the capture zone, h_(s) asafety height, g the terrestrial acceleration and K an adaptationconstant.
 4. A device for automatic navigation assistance for anaircraft having a program memory, comprising: the program memory has aprogram for computing the width of a capture zone, a capture zone beinga zone in which the aircraft can capture a predetermined verticalprofile segment by applying a transition between the guidance submodewhich the aircraft is in and the guidance submode adapted to thefollowing of the profile segment to be captured, the width of thecapture zone being calculated as a function of the height h of thevertical profile to be captured and of the speed v which the aircrafthas when plumb with this height when the aircraft is not on the profileor at this height when the aircraft is on the profile.
 5. The device asclaimed in claim 4, wherein the program memory includes a program forcomputing the width of a capture zone as a function of the height h andof the square of the speed v.
 6. The method as claimed in claim 2,wherein the width of the capture zone is equal to around 2Δh with${\Delta\quad h} = {{h^{\prime} - h} = {h_{s} + {\left\lbrack {h + \frac{v^{2}}{2g}} \right\rbrack\frac{1}{K}}}}$h′ being the height of the upper bound of the capture zone, h_(s) asafety height, g the terrestrial acceleration and K an adaptationconstant.